1. Check the ink cartridge and print head. Some printers have a separate print head that gets clogged.
    
2. The print head might get clogged if you turn off your printer using the surge protector power switch.

   When your ink-jet printer or plotter is turned off or not in use, the ink head returns to a "rest" position, capping the heads. When ink cakes on this assembly, air flows to the heads and dries them out.

   Always turn your printer off using the printer power switch so the print head will cap correctly, preventing your ink from drying out.
    

3. Use the ink recommended by your printer's manufacturer. Other brands could, and usually do, leak because of poor quality control.

   Don't mix brands or colors of inks. The chemical composition is different for each one and mixing them can affect print quality.

   If you refill ink cartridges with aftermarket ink, be aware that the cartridge may contain a bad head. Simply refilling a faulty cartridge won't work -- you'll need to change it.
    

4. Always cover the print head surface with scotch tape or with the Mylar tape supplied with the cartridge and place it in a Ziploc bag to prevent it from drying out. If you want to clean the surface of the head, use alcohol on a lint-free cloth.
    
5. Cover the printer when it's not being used. Most ink-jet printers feed paper from the top, and the opening collects dust, paperclips, and so on. Store the head as mentioned above if you're not going to use the printer for a while. You should use your ink-jet printer once a week to keep the ink flowing.

Secret stuff

All ink-jet printers and plotters have hidden commands that can be activated using the control buttons on the printer or plotter. Press Power, Form Feed, or Line Feed to activate calibration menus, demos, and setup values. Be careful here -- you might mess up factory settings required for correct printing.